Updated 07/10/2025 to clarify that the third annual Contrails Workshop was arranged by contrails.org, and this year took place at Imperial College London.
Aviation’s climate conversation has long centred on CO2 mitigation, but non-CO2 impacts, particularly contrails, are now moving rapidly up the agenda. Updated aviation climate roadmaps, including most recently the International Council on Clean Transportation’s (ICCT) Aviation Vision 2050 roadmap, are increasingly pointing to non-CO2 impacts as an area for achievable short and medium-term action. More broadly, industry attention in contrail science is growing, particularly in Europe where the EU’s first non-CO2 monitoring framework is compelling airlines to monitor non-CO2 impacts.
Often described as aviation’s climate problem’s ‘low-hanging fruit’, contrails could be avoided with modest flight-planning changes, at costs far below SAF, and with almost-immediate climate benefits (see Ishka SAVi’s first briefing on contrails for more details).
Five years after EASA’s report highlighted the climate-warming potential of contrails, Ishka investigates in this two-part series why so little has happened since – and whether Europe’s regulatory push could change that.
Recap: the case for contrail action
Contrails form when jet engine exhaust meets cold, humid air at cruising altitude. Most vanish quickly, but under specific atmospheric conditions, some can persist and spread into cirrus clouds that trap heat at night. As a result, their contribution to aviation’s warming effect operates on a different timescale to CO2, hours to days rather than centuries. “If we consistently avoid making contrails, we effectively cool down the planet almost immediately,” underlines Joachim Majholm, founder of Blue Lines, an environmental advocacy group focused on contrails. “This is very unique. CO2 warms very slowly over hundreds of years, but the warming contrails produce is massive compared to CO2.”
The ICCT’s revised modelling, released last month, estimates that contrail avoidance alone accounts for 40%–43% of avoidable aviation warming by 2050. By comparison, SAF contributes around 21% and hydrotreating fossil jet fuel and operational efficiency about 11% each. The report puts contrail avoidance at about $5–$20 per tonne CO2 equivalent, compared with more than $300 for SAF. On a fleetwide basis, avoiding 95% of contrails from flights leaving high- and upper-middle-income countries would add about 1% to fuel burn.
Unlike other aviation emissions, the most climate-impactful contrails are highly concentrated in certain regions. Estuaire, a climate-impact data platform focused on reducing aviation emissions, estimated that in 2023, just 2.9% of global flights generated 80% of contrail radiative forcing. Avoiding them, would require an increase in fuel consumption of only 0.4%-0.5%, Estuaire estimates. “So, a few hundred kilos if not tens of kilos of extra kerosene, and on some specific flights you can get back 20 times the amount in terms of climate savings. That's why it's a low hanging fruit,” explains Estuaire CEO Maxime Meijers.
Contrail avoidance through rerouting or altitude changes is the most effective lever. But other measures also contribute. Studies show that low-aromatic fuels – whether SAF or hydrotreated fossil jet fuel, such as a batch recently purchased by Airbus – can reduce contrail formation. “Engine types seem to have a large impact on contrail warming,” Majholm also observed, as illustrated by Imperial College London findings, although tactical avoidance still offers the fastest global solution.
Challenges – and their possible solutions
If the case for contrail avoidance is so strong, why has action been limited?
Remaining scientific uncertainty
Industry scepticism of action on contrails has long been based on two key uncertainties: the true scale of contrails’ climate impact, and the accuracy of prediction models. “What is the precise climate impact? Is it big, like half of CO2, or huge, twice as big? That is still the question,” Majholm concedes, but he insists that either way, “it is big enough for us to address it.”
On the modelling side, re-routing flights to avoid contrail susceptible zones requires identifying thin, shifting layers of very cold, humid air where persistent contrails form. Boundaries can be unclear, which complicates dispatch decisions. “A lot of work is going on all over Europe and the US to get better at predicting the zones, […] the models are improving,” Majholm explains, reflecting on takeaways from contrails.org’s third annual Contrails Workshop, held at Imperial College London in September.
Lack of regulation
With the science maturing, the larger barrier is now funding for airlines. “The feedback of the industry is moving from ‘there’s not enough data’ to ‘there’s not enough incentives,’” explains Meijers, whose company supplies data and builds contrail avoidance systems.
Tactical avoidance – minor altitude or route adjustments to bypass contrail-prone layers – is the most immediate lever and the one most likely to scale quickly once air traffic control (ATC) actively manages it or suitable operator incentives exist. However, operators lack an economic incentive without a mechanism to offset the fuel penalty that arises from diverting from flight plans.
“Airlines have large expenses. It’s as simple as that […] if you don’t have that small incentive that pays for the extra fuel, even burning tens of kilos of extra kerosene on a short-haul flight is not in anyone’s interest to do.”
As for airline sustainability reporting, while some airlines have made contrail mitigation efforts part of their sustainability narrative, most find themselves unable to account for contrail action. Contrails are also not counted in the Science Based Targets Initiative (SBTi) or other voluntary frameworks, so there is currently little incentive to feature them from an ESG reporting perspective.
Operational scale-up
Securing broad participation is further complicated by the economic reality that contrail avoidance will most likely never resemble a multi-billion-dollar industry. Unlike SAF, which “attracts capital because it is a guaranteed product, every flight needs fuel, and mandates create demand”, for contrail avoidance “you just need a prediction software function in your flight planning [...] That is not a multi-billion-dollar business,” argues Majholm.
This limited commercial upside means there is little financial incentive for industry players to fund extensive flight trials, slowing progress toward large-scale implementation. In the absence of regulatory incentives, Meijers points to Europe’s ETS-funded Innovation Fund, SESAR (Single European Sky ATM Research, the technological pillar of the Single European Sky), or similar vehicles as possible financing mechanisms for large-scale contrail flight trials.
The Ishka View
It’s still early days for aviation’s non-CO2 mitigation, but in a hard-to-abate sector, it stands out for being implementable at low cost, with near-term effect. An expected part of this implementation must be large scale contrail avoidance trials, to test the operationalisation through re-routing. Such trials have long been demanded by academics studying the issue, but without a mechanism to cover small fuel penalties, operators have little economic incentive to act.
This is the first of a two-part series examining the status of efforts to mitigate contrails’ climate impact. The second part explores whether Europe’s regulatory push could change that.
